CA2691299C - High specific surface area mixed oxide of cerium and of another rare earth, preparation method and use in catalysis - Google Patents
High specific surface area mixed oxide of cerium and of another rare earth, preparation method and use in catalysis Download PDFInfo
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- CA2691299C CA2691299C CA2691299A CA2691299A CA2691299C CA 2691299 C CA2691299 C CA 2691299C CA 2691299 A CA2691299 A CA 2691299A CA 2691299 A CA2691299 A CA 2691299A CA 2691299 C CA2691299 C CA 2691299C
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- 229910052761 rare earth metal Inorganic materials 0.000 title claims abstract description 23
- 150000002910 rare earth metals Chemical class 0.000 title claims abstract description 21
- 229910052684 Cerium Inorganic materials 0.000 title claims description 15
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 title description 14
- 238000002360 preparation method Methods 0.000 title description 11
- 238000006555 catalytic reaction Methods 0.000 title description 7
- 238000001354 calcination Methods 0.000 claims abstract description 31
- 239000003054 catalyst Substances 0.000 claims abstract description 16
- 239000007788 liquid Substances 0.000 claims abstract description 15
- 229910000420 cerium oxide Inorganic materials 0.000 claims abstract description 14
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000002244 precipitate Substances 0.000 claims abstract description 14
- 150000001875 compounds Chemical class 0.000 claims abstract description 11
- 150000001785 cerium compounds Chemical class 0.000 claims abstract description 7
- 239000000203 mixture Substances 0.000 claims description 74
- 238000000034 method Methods 0.000 claims description 23
- 239000011148 porous material Substances 0.000 claims description 13
- 230000003197 catalytic effect Effects 0.000 claims description 10
- 238000002485 combustion reaction Methods 0.000 claims description 5
- 239000007789 gas Substances 0.000 claims description 5
- 239000012429 reaction media Substances 0.000 claims description 5
- XMPZTFVPEKAKFH-UHFFFAOYSA-P ceric ammonium nitrate Chemical compound [NH4+].[NH4+].[Ce+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O XMPZTFVPEKAKFH-UHFFFAOYSA-P 0.000 claims description 4
- 229910052746 lanthanum Inorganic materials 0.000 claims description 4
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims description 4
- 229910052777 Praseodymium Inorganic materials 0.000 claims description 3
- 150000001242 acetic acid derivatives Chemical class 0.000 claims description 3
- 150000001805 chlorine compounds Chemical class 0.000 claims description 3
- 150000002823 nitrates Chemical class 0.000 claims description 3
- PUDIUYLPXJFUGB-UHFFFAOYSA-N praseodymium atom Chemical compound [Pr] PUDIUYLPXJFUGB-UHFFFAOYSA-N 0.000 claims description 3
- 229910052727 yttrium Inorganic materials 0.000 claims description 3
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims description 3
- 229910052779 Neodymium Inorganic materials 0.000 claims description 2
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 claims description 2
- 150000003467 sulfuric acid derivatives Chemical class 0.000 claims description 2
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 claims 1
- 238000010438 heat treatment Methods 0.000 abstract description 13
- 239000000243 solution Substances 0.000 description 35
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 19
- 239000002609 medium Substances 0.000 description 19
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 14
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 12
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 12
- 235000011114 ammonium hydroxide Nutrition 0.000 description 12
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 11
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 9
- 229910002651 NO3 Inorganic materials 0.000 description 8
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 6
- 239000000047 product Substances 0.000 description 6
- 150000007514 bases Chemical class 0.000 description 5
- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 5
- -1 inorganic acid salt Chemical class 0.000 description 5
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical compound [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- MMKQUGHLEMYQSG-UHFFFAOYSA-N oxygen(2-);praseodymium(3+) Chemical compound [O-2].[O-2].[O-2].[Pr+3].[Pr+3] MMKQUGHLEMYQSG-UHFFFAOYSA-N 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 229910003447 praseodymium oxide Inorganic materials 0.000 description 4
- YWECOPREQNXXBZ-UHFFFAOYSA-N praseodymium(3+);trinitrate Chemical compound [Pr+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O YWECOPREQNXXBZ-UHFFFAOYSA-N 0.000 description 4
- 239000000376 reactant Substances 0.000 description 4
- 238000006722 reduction reaction Methods 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- 229940044927 ceric oxide Drugs 0.000 description 3
- 238000000975 co-precipitation Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 150000000703 Cerium Chemical class 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 2
- 150000001412 amines Chemical group 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 238000004581 coalescence Methods 0.000 description 2
- 239000000084 colloidal system Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- KTUFCUMIWABKDW-UHFFFAOYSA-N oxo(oxolanthaniooxy)lanthanum Chemical compound O=[La]O[La]=O KTUFCUMIWABKDW-UHFFFAOYSA-N 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 238000002459 porosimetry Methods 0.000 description 2
- ZLGIGTLMMBTXIY-UHFFFAOYSA-K praseodymium(3+);trihydroxide Chemical class [OH-].[OH-].[OH-].[Pr+3] ZLGIGTLMMBTXIY-UHFFFAOYSA-K 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 229910001854 alkali hydroxide Inorganic materials 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910001860 alkaline earth metal hydroxide Inorganic materials 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- ILRRQNADMUWWFW-UHFFFAOYSA-K aluminium phosphate Chemical class O1[Al]2OP1(=O)O2 ILRRQNADMUWWFW-UHFFFAOYSA-K 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-O ammonium group Chemical group [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- 239000012736 aqueous medium Substances 0.000 description 1
- 239000008346 aqueous phase Substances 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000004202 carbamide Substances 0.000 description 1
- 238000004517 catalytic hydrocracking Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000004320 controlled atmosphere Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000006356 dehydrogenation reaction Methods 0.000 description 1
- 238000006704 dehydrohalogenation reaction Methods 0.000 description 1
- 238000007324 demetalation reaction Methods 0.000 description 1
- 238000007323 disproportionation reaction Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 238000006317 isomerization reaction Methods 0.000 description 1
- YXEUGTSPQFTXTR-UHFFFAOYSA-K lanthanum(3+);trihydroxide Chemical class [OH-].[OH-].[OH-].[La+3] YXEUGTSPQFTXTR-UHFFFAOYSA-K 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 150000007524 organic acids Chemical class 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 235000021317 phosphate Nutrition 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000002407 reforming Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000004071 soot Substances 0.000 description 1
- 229910052566 spinel group Inorganic materials 0.000 description 1
- 238000010561 standard procedure Methods 0.000 description 1
- 238000000629 steam reforming Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/10—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of rare earths
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
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- C01F17/00—Compounds of rare earth metals
- C01F17/20—Compounds containing only rare earth metals as the metal element
- C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
- C01F17/224—Oxides or hydroxides of lanthanides
- C01F17/235—Cerium oxides or hydroxides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
- B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/002—Mixed oxides other than spinels, e.g. perovskite
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- B01J37/02—Impregnation, coating or precipitation
- B01J37/03—Precipitation; Co-precipitation
- B01J37/031—Precipitation
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- B01J37/08—Heat treatment
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- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F17/00—Compounds of rare earth metals
- C01F17/20—Compounds containing only rare earth metals as the metal element
- C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
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- C01F17/00—Compounds of rare earth metals
- C01F17/20—Compounds containing only rare earth metals as the metal element
- C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
- C01F17/241—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion containing two or more rare earth metals, e.g. NdPrO3 or LaNdPrO3
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Abstract
The mixed oxide of the invention mainly consists of cerium oxide and of at least one oxide of another rare earth. It has a specific surface area of at least 20 m2/g after calcining at 1000° C for 5 hours. It is obtained by forming a liquid medium comprising a cerium compound; by heating this medium; by adding to the precipitate obtained a compound of the other rare earth, by heating the medium thus obtained and by bringing its pH to a basic value and by calcining the precipitate. The mixed oxide may be used as a catalyst support.
Description
DESCRIPTION
HIGH SPECIFIC SURFACE AREA MIXED OXIDE OF CERIUM AND OF
ANOTHER RARE EARTH, PREPARATION METHOD AND USE IN CATALYSIS
Technical Field The present invention relates to a high specific surface area mixed oxide of cerium and of another rare earth, to its preparation method and to its use in catalysis.
Background Art It is known that ceric oxide may be used as a catalyst or catalyst support. It is also well known that the effectiveness of a catalyst generally increases as the contact area between the catalyst and the reactants increases. In order to achieve this, it is necessary that the catalyst be kept in a state which is as finely divided as possible, that is to say that the solid particles which constitute it are as small and as individualized as possible. The fundamental role of the support is therefore to keep the catalyst particles or crystallites in contact with the reactant, in the most finely divided state possible.
During the prolonged use of a catalyst support, a reduction in the specific surface area occurs due to the coalescence of the porosity of the product. During this coalescence, some of the catalyst is encompassed in the bulk of the support and can no longer be in contact with the reactants.
HIGH SPECIFIC SURFACE AREA MIXED OXIDE OF CERIUM AND OF
ANOTHER RARE EARTH, PREPARATION METHOD AND USE IN CATALYSIS
Technical Field The present invention relates to a high specific surface area mixed oxide of cerium and of another rare earth, to its preparation method and to its use in catalysis.
Background Art It is known that ceric oxide may be used as a catalyst or catalyst support. It is also well known that the effectiveness of a catalyst generally increases as the contact area between the catalyst and the reactants increases. In order to achieve this, it is necessary that the catalyst be kept in a state which is as finely divided as possible, that is to say that the solid particles which constitute it are as small and as individualized as possible. The fundamental role of the support is therefore to keep the catalyst particles or crystallites in contact with the reactant, in the most finely divided state possible.
During the prolonged use of a catalyst support, a reduction in the specific surface area occurs due to the coalescence of the porosity of the product. During this coalescence, some of the catalyst is encompassed in the bulk of the support and can no longer be in contact with the reactants.
The known ceric oxides have a specific surface area which decreases rapidly for operating temperatures above 500 C and which may be very low at even higher temperatures, that is to say between 900 C and 1000 C. Therefore, these oxides can no longer be used under these temperature conditions.
Disclosure of the Invention Problem to be solved by the Invention There is therefore a need for ceric oxides which are effective as a. catalyst or catalyst support in high temperature ranges.
The object of the invention is to provide such oxides.
Means for solving Problem For this purpose, the composition of the invention is of the type mainly consisting of cerium oxide and of at least one oxide of another rare earth, and it is characterized in that it has a specific surface area of at least 20 m2/g after calcining at 1000 C for 5 hours.
Best Mode for Carrying Out the Invention The composition of the invention thus has a greater surface area even at a particularly high temperature.
Other features, details and advantages of the invention will become even more fully apparent on reading the description which follows and also the concrete but non-limiting examples intended to illustrate it.
For the remainder of the description, the expression "specific surface area" is understood to mean the BET
Disclosure of the Invention Problem to be solved by the Invention There is therefore a need for ceric oxides which are effective as a. catalyst or catalyst support in high temperature ranges.
The object of the invention is to provide such oxides.
Means for solving Problem For this purpose, the composition of the invention is of the type mainly consisting of cerium oxide and of at least one oxide of another rare earth, and it is characterized in that it has a specific surface area of at least 20 m2/g after calcining at 1000 C for 5 hours.
Best Mode for Carrying Out the Invention The composition of the invention thus has a greater surface area even at a particularly high temperature.
Other features, details and advantages of the invention will become even more fully apparent on reading the description which follows and also the concrete but non-limiting examples intended to illustrate it.
For the remainder of the description, the expression "specific surface area" is understood to mean the BET
specific surface area determined by nitrogen absorption in accordance with the ASTM D 3663-78 standard established from the Brunauer-Emmett-Teller method described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)".
Similarly, the expression "rare earth" is understood to mean the elements from the group made up of yttrium and the elements from the Periodic Table with atomic numbers between 57 and 71 inclusive.
Moreover, the calcinations, at the end of which the surface area values are given, are calcinations in air.
Furthermore, the specific surface area values which are indicated for a given temperature and a given time correspond, unless otherwise indicated, to calcinations at a temperature hold over the time indicated.
The contents are given as oxides unless otherwise indicated. The cerium oxide is in the form of ceric oxide, the oxides of the other rare earths are in the Ln203 form, unless indicated otherwise, Ln denoting the rare earth.
The composition of the invention mainly consists of cerium oxide and of one or more oxides of a rare earth. In the remainder of the description, use will be made, for convenience, of the terms "rare earth" in the singular, but these terms should be understood, unless otherwise indicated, as applying both to the case where a single rare earth is present in the composition and to the case where several rare earths are also present.
The expression "mainly consists" is understood to mean that the composition in question only contains the oxides of the aforementioned elements, cerium and another rare earth and that it does not contain an oxide of another element, in particular such as zirconium, capable of having a positive influence on the stability of the specific surface area of the composition. On the other hand, the composition may contain elements such as impurities which may especially originate from its preparation method, for example raw materials or starting reactants used.
According to particular embodiments of the invention, the rare earth may be yttrium, neodymium, lanthanum or praseodymium. According to another embodiment, lanthanum and praseodymium are present in combination in the composition.
The content of rare-earth oxide is generally at most 25%, preferably when the rare earth is lanthanum, more particularly at most 20% and preferably at most 15% by weight. The minimum content is not critical but generally it is at least 1%, more particularly at least 2% and preferably at least 5% by weight. This content is expressed as oxide of the rare earth relative to the weight of the whole composition.
The composition of the invention may additionally have a specific surface area of at least 22 m2/g after calcining at 1000 C for 5 hours. More generally, values of at least around 25 m2/g may be obtained under the same calcination conditions.
The specific surface area of the composition of the invention may remain as high even at a higher temperature still. Thus, this surface area may be at least 10 m 2/g, more particularly at least 14 m2/g after calcining at 1100 C for 5 hours.
Finally, the composition of the invention may have a specific surface area of at least 30 m2/g after calcining at 900 C for 5 hours. More generally, values of at least around 35 m2/g may be obtained under the same calcination conditions.
The compositions of the invention are also characterized by their porosity. Specifically they have, even at high temperature, porosities which are high and which are provided by pores, the size of which is at most 200 nm. In other words, the compositions of the invention are characterized by a high mesoporosity.
The porosities indicated in the present description are measured by mercury intrusion porosimetry in accordance with the ASTM D 4284-03 standard (Standard method for determining pore volume distribution of catalysts by mercury intrusion porosimetry). More specifically, these compositions have, after calcining at 1000 C for 5 hours, a porosity provided by pores having a diameter of at most 200 nm which is at least 0.15 cm3/g, more particularly at least 0.2 cm3/g. Moreover, these same compositions may have, after calcining at 1000 C for 5 hours, a porosity of at least 0.10 cm3/g, more particularly of at least 0.15 cm3/g;
this porosity being provided by pores having a diameter of at most 50 nm.
It should also be noted that the compositions of the invention have substantially identical porosities after calcining at 900 C for 5 hours. In other words, the porosity of the compositions of the invention practically does not vary after calcining at 900 C then at 1000 C for 5 hours. This applies most particularly to the porosity provided by the pores of at most 200 nm. Specifically, in this case, the reduction in the porosity is generally at most 10%, preferably at most 5%.
The method for preparing the composition of the invention will now be described.
This method is characterized in that it comprises the following steps:
- a liquid medium comprising a cerium compound is formed;
- the medium is heated at a temperature of at least 100 C;
- the precipitate obtained at the end of the preceding step is separated from the liquid medium, a compound of the other rare earth is added thereto and another liquid medium is formed;
- the medium thus obtained is heated at a temperature of at least 100 C;
- the reaction medium obtained at the end of the preceding heating step is brought to a basic pH; and - the precipitate derived from the preceding step is separated and is calcined.
The first step of the method therefore consists in forming a liquid medium comprising a cerium compound.
The liquid medium is generally water.
The cerium compound is preferably chosen from soluble compounds. It may especially be an organic or inorganic acid salt such as a nitrate, a sulphate, an acetate, a chloride or a ceric ammonium nitrate.
Preferably, ceric nitrate is used. It is advantageous to use salts with a purity of at least 99.5o and more particularly of at least 99.9%. An aqueous ceric nitrate solution can, for example, be obtained by reaction of nitric acid with a hydrated ceric oxide prepared conventionally by reaction of a solution of a cerous salt, for example cerous nitrate, and of an aqueous ammonia solution in the presence of aqueous hydrogen peroxide solution. It is also possible, preferably, to use a ceric nitrate solution obtained according to the method for electrolytic oxidation of a cerous nitrate solution, as described in the document FR-A-2 570 087, and which constitutes in this instance an advantageous starting material.
It should be noted in this instance that the aqueous solutions of cerium salts may exhibit a degree of initial free acidity which can be adjusted by the addition of a base or of an acid. However, it is just as possible to use an initial solution of cerium salts effectively exhibiting a degree of free acidity as mentioned above, as solutions which will have been neutralized beforehand more or less exhaustively. This neutralization can be carried out by addition of a basic compound to the abovementioned mixture, so as to limit this acidity. This basic compound can, for example, be an aqueous ammonia solution or else a solution of alkali metal (sodium, potassium, and the like) hydroxides but preferably an aqueous ammonia solution.
Finally, it should be noted that, when the starting mixture comprises cerium mainly in the III form, it is preferable to involve, in the course of the method, an oxidizing agent, for example aqueous hydrogen peroxide solution.
It is also possible to use a sol as starting compound for the cerium. The term "sol" denotes any system composed of fine solid particles of colloidal dimensions, that is to say of dimensions between approximately 1 nm and approximately 500 nm, based on a cerium compound, this compound generally being a cerium oxide and/or a hydrated cerium oxide in suspension in a liquid aqueous phase, it additionally being possible for said particles optionally to comprise residual amounts of bonded or adsorbed ions, such as, for example, nitrates, acetates, chlorides or ammoniums. It should be noted that, in such a sol, the cerium may be found either completely in the form of colloids or simultaneously in the form of ions and in the form of colloids.
The mixture can without distinction be obtained either from compounds initially in the solid state which will be subsequently introduced into the bottom of a water vessel, for example, or else directly from solutions of these compounds.
The second step of the method consists in heating the medium prepared in the preceding step at a temperature of at least 100 C.
The temperature at which the medium is heated is generally between 100 C and 150 C, and more particularly between 110 C and 130 C. The heating operation can be carried out by introducing the liquid medium into a sealed chamber (closed reactor of the autoclave type). Under the temperature conditions given above, and in an aqueous medium, it is thus possible to specify, by way of illustration, that the pressure in the closed reactor can vary between a value of greater than 1 bar (105 Pa) and 165 bar (1.65 x 10' Pa), preferably between 5 bar (5 x 10s Pa) and 165 bar (1.65 x 10 7 Pa). The heating can also be carried out in an open reactor for temperatures in the vicinity of 100 C.
The heating can be carried out either in air or under an inert gas atmosphere, preferably nitrogen.
The duration of the heating can vary within wide limits, for example between 30 minutes and 48 hours, preferably between 1 and 5 hours. Likewise, the rise in temperature is carried out at a rate which is not critical and it is thus possible to reach the reaction temperature set by heating the medium, for example, between 30 minutes and 4 hours, these values being given entirely by way of indication.
At the end of the heating step a precipitate is obtained which is separated from the liquid medium by any suitable means, for example by decanting the mother liquors.
Added to the precipitate thus separated is a compound of the other rare earth, forming a second liquid medium.
The rare-earth compound may be of the same nature as the cerium compound used in the first step of the method.
That which has been described above for this compound therefore applies here to the rare-earth compound which may more particularly be chosen from nitrates, sulphates, acetates and chlorides.
In another step of the method, the second liquid medium is heated at a temperature of at least 100 C.
Here too, that which has been described above for the first heating step likewise applies here for the second heating step.
At the end of this second heating step, the reaction medium obtained is brought to a basic pH. In order to do this, a basic compound is introduced into the reaction medium. It is possible to use, as a base or basic compound, hydroxide type products. Mention may be made of alkali or alkaline-earth metal hydroxides. It is also possible to use secondary, tertiary or quaternary amines. However, amines and aqueous ammonia may be preferred insofar as they reduce the risks of contamination by the alkali or alkaline-earth metal cations. Mention may also be made of urea. The basic compound may more particularly be used in the form of a solution.
The pH value to which the medium is brought may more particularly be between 8 and 10, more particularly 8 and 9.
In a final step of the method according to the invention, the precipitate recovered is subsequently calcined. This calcining makes it possible to develop the crystallinity of the product formed and it can also be adjusted and/or chosen according to the subsequent operating temperature intended for the composition according to the invention, this being done while taking into account the fact that the specific surface area of the product decreases as the calcining temperature employed increases. Such a calcination is generally carried out in air but a calcination carried out, for example, in an inert gas or in a controlled atmosphere (oxidizing or reducing) is very clearly not excluded.
In practice, the calcining temperature is generally limited to a range of values of between 300 C and 1000 C.
The compositions of the invention can be used as catalysts or catalyst supports. Thus, the invention also relates to catalytic systems comprising the compositions of the invention. For such systems, these compositions can thus be applied to any support commonly used in the field of catalysis, that is to say thermally inert supports in particular. This support can be chosen from alumina, titanium oxide, zirconium oxide, silica, spinels, zeolites, silicates, crystalline silicoaluminium phosphates or crystalline aluminium phosphates.
The compositions can also be used in catalytic systems comprising a coating (wash coat) possessing catalytic properties and based on these compositions, on a substrate of the, for example, metal or ceramic monolith type. The coating can itself also comprise a support of the type of those mentioned above. This coating is obtained by mixing the composition with the support, so as to form a suspension which can subsequently be deposited on the substrate.
These catalytic systems and more particularly the compositions of the invention can have a great many applications. They are therefore particularly well suited to, and thus usable in, the catalysis of various reactions, such as, for example, dehydration, hydrosulphurization, hydrodenitrification, desulphurization, hydrodesulphurization, dehydrohalogenation, reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, dismutation, oxychlorination, dehydrocyclization of hydrocarbons or other organic compounds, oxidation and/or reduction reactions, the Claus reaction, treatment of exhaust gases from internal combustion engines, diesel or petrol engines, demetallation, methanation, the shift conversion or water gas shift or the catalytic oxidation of the soot emitted by internal combustion engines, such as diesel engines or petrol engines operating under lean burn conditions. Finally, the catalytic systems and the compositions of the invention can be used as NOX traps or for promoting the reduction of NOX, even in an oxidizing environment.
In the case of these uses in catalysis, the compositions of the invention are employed in combination with precious metals. They thus act as support for these metals. The nature of these metals and the techniques for the incorporation of the latter in the support compositions are well known to a person skilled in the art. For example, the metals can be platinum, rhodium, palladium or iridium.
They can in particular be incorporated in the compositions by impregnation.
Among the uses mentioned, treatment of the exhaust gases from internal combustion engines (automobile postcombustion catalysis) constitutes a particularly advantageous application. For this reason, the invention also relates to a method for treating the exhaust gases from internal combustion engines which is characterized in that use is made, as catalyst, of a catalytic system as described above or of a composition according to the invention and as described above.
Examples Examples will now be given.
This example relates to the preparation of a composition based on cerium oxide and on lanthanum oxide in a proportion, by weight of oxide, of 90/10 respectively.
200 ml of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.1 ml of a 25% aqueous ammonia solution, then diluted with 794.9 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 20.5 ml of a lanthanum nitrate solution containing 5.16 g of La203 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The solution was then heated at 120 C for 2 hours. After cooling the solution to 85 C, a 25% aqueous ammonia solution was added, with stirring, in order to adjust the pH to 8.5. The suspension obtained was filtered over a Nutsche filter to obtain a precipitate. The precipitate was calcined in air at 300 C for 10 hours to obtain a composition containing 10 wt% of La203 and 90 wt%
of Ce02.
This example relates to the preparation of a composition based on cerium oxide and on praseodymium oxide in a proportion, by weight of oxide, of 90/10 respectively.
197.6 of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.6 ml of a 25% aqueous ammonia solution, then diluted with 796.8 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 11.0 ml of a praseodymium nitrate solution containing 5.25 g of Pr6011 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The procedure as in Example 1 was then followed to obtain a composition containing 10 wt% of Pr6011 and 90 wt% of Ce02 .
This example relates to the preparation of a composition based on cerium oxide, lanthanum oxide and praseodymium oxide in a proportion, by weight of oxide, of 90/5/5 respectively.
201.6 ml of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.7 ml of a 25% aqueous ammonia solution, then diluted with 792.7 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 6.1 ml of a lanthanum nitrate solution containing 2.63 g of La203 and 5.3 ml of a praseodymium nitrate solution containing 2.63 g of Pr6011 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The procedure as in Example 1 was then followed to obtain a composition containing 5 wt% of La203, 5 wt% of Pr6011 and 90 wt% of Ce02.
This example relates to the preparation of a composition based on cerium oxide and lanthanum oxide in a proportion by weight of oxide of 80/20 respectively.
197.6 ml of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.6 ml of a 25% aqueous ammonia solution, then diluted with 796.8 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 46.1 ml of a lanthanum nitrate solution containing 11.60 g of La203 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The procedure as in Example 1 was then followed to obtain a composition containing 20 wt% of La203 and 80 wt% of Ce02 .
This example relates to the preparation, by a coprecipitation method, of a composition based on cerium oxide and lanthanum oxide in a proportion, by weight of oxide, of 90/10 respectively.
35.5 ml of a cerous nitrate solution containing 18 g of CeOzr 7.9 ml of a lanthanum nitrate solution containing 2.0 g of La2O3 and 356.6 ml of pure water were mixed together.
Introduced into this mixture were 400 ml of a 10% aqueous ammonia solution over 10 minutes, with stirring, to precipitate cerium and lanthanum hydroxides. The pH after precipitation was 10. The precipitate was filtered over a Nutsche filter and calcined in air at 300 C for 10 hours to obtain a composition containing 10 wt% of La2O3 and 90 wt%
of CeO2.
This example relates to the preparation, by a coprecipitation method, of a composition based on cerium oxide and praseodymium oxide in a proportion, by weight of oxide, of 90/10 respectively.
35.5 ml of a cerous nitrate solution containing 18 g of Ce02r 4.0 ml of a praseodymium nitrate solution containing 2.0 g of Pr6011 and 360.5 ml of pure water were mixed together. Introduced into this mixture were 400 ml of a 10%
aqueous ammonia solution over 10 minutes, with stirring, to precipitate cerium and praseodymium hydroxides. The pH
after precipitation was 10. The procedure as in Comparative Example 5 was then followed to obtain a composition containing 10 wt% of Pr6011 and 90 wt% of Ce02.
This example relates to the preparation, by a coprecipitation method, of a composition based on cerium oxide, lanthanum oxide and praseodymium oxide in a proportion, by weight of oxide, of 90/5/5 respectively.
35.5 ml of a cerous nitrate solution containing 18 g of CeO2, 4.0 ml of a lanthanum nitrate solution containing 1.0 g of La203r 2.0 ml of a praseodymium nitrate solution containing 1.0 g of Pr6011 and 358.5 ml of pure water were mixed together. Introduced into this mixture were 400 ml of a 10% aqueous ammonia solution over 10 minutes, with stirring, to precipitate cerium and praseodymium hydroxides.
The pH after precipitation was 10. The procedure as in Comparative Example 5 was then followed to obtain a composition containing 5 wt% of La203, 5 wt% of Pr6011 and 90 wt% of CeOZ .
Given in Table 1 below are the specific surface areas of the products from the various examples.
Table 1 Specific surface area (m /g) Example 300 C 10 900 C 5 h 1000 C 5 1100 C 5 h h h comparative 6 70 6 2 < 1 comparative 7 71 7 3 < 1 comparative Given in Table 2 below are the porosity characteristics of the products from the various examples.
These porosities were measured with a CE Instruments Pascal 240 machine.
. _., _. .~v ~.., ......,VV
Table 2 Porosity (CM3 /g) After calcination 900 C After calcination 5h 1000 C 5h Porosity Porosity Porosity Example Porosity provided provided provided provided by by pores by pores by pores pores of at of at of at most of at most most 200 nm most 50 200 nm 50 nm nm 1 0.21 0.19 0.20 0.17 2 0.23 0.20 0.22 0.15 3 0.25 0.21 0.24 0.19 4 0.21 0.19 0.22 0.18 0.08 0.06 0.06 0.02 comparative 6 0.06 0.04 0.05 0.03 comparative 7 0.07 0.05 0.06 0.04 comparative
Similarly, the expression "rare earth" is understood to mean the elements from the group made up of yttrium and the elements from the Periodic Table with atomic numbers between 57 and 71 inclusive.
Moreover, the calcinations, at the end of which the surface area values are given, are calcinations in air.
Furthermore, the specific surface area values which are indicated for a given temperature and a given time correspond, unless otherwise indicated, to calcinations at a temperature hold over the time indicated.
The contents are given as oxides unless otherwise indicated. The cerium oxide is in the form of ceric oxide, the oxides of the other rare earths are in the Ln203 form, unless indicated otherwise, Ln denoting the rare earth.
The composition of the invention mainly consists of cerium oxide and of one or more oxides of a rare earth. In the remainder of the description, use will be made, for convenience, of the terms "rare earth" in the singular, but these terms should be understood, unless otherwise indicated, as applying both to the case where a single rare earth is present in the composition and to the case where several rare earths are also present.
The expression "mainly consists" is understood to mean that the composition in question only contains the oxides of the aforementioned elements, cerium and another rare earth and that it does not contain an oxide of another element, in particular such as zirconium, capable of having a positive influence on the stability of the specific surface area of the composition. On the other hand, the composition may contain elements such as impurities which may especially originate from its preparation method, for example raw materials or starting reactants used.
According to particular embodiments of the invention, the rare earth may be yttrium, neodymium, lanthanum or praseodymium. According to another embodiment, lanthanum and praseodymium are present in combination in the composition.
The content of rare-earth oxide is generally at most 25%, preferably when the rare earth is lanthanum, more particularly at most 20% and preferably at most 15% by weight. The minimum content is not critical but generally it is at least 1%, more particularly at least 2% and preferably at least 5% by weight. This content is expressed as oxide of the rare earth relative to the weight of the whole composition.
The composition of the invention may additionally have a specific surface area of at least 22 m2/g after calcining at 1000 C for 5 hours. More generally, values of at least around 25 m2/g may be obtained under the same calcination conditions.
The specific surface area of the composition of the invention may remain as high even at a higher temperature still. Thus, this surface area may be at least 10 m 2/g, more particularly at least 14 m2/g after calcining at 1100 C for 5 hours.
Finally, the composition of the invention may have a specific surface area of at least 30 m2/g after calcining at 900 C for 5 hours. More generally, values of at least around 35 m2/g may be obtained under the same calcination conditions.
The compositions of the invention are also characterized by their porosity. Specifically they have, even at high temperature, porosities which are high and which are provided by pores, the size of which is at most 200 nm. In other words, the compositions of the invention are characterized by a high mesoporosity.
The porosities indicated in the present description are measured by mercury intrusion porosimetry in accordance with the ASTM D 4284-03 standard (Standard method for determining pore volume distribution of catalysts by mercury intrusion porosimetry). More specifically, these compositions have, after calcining at 1000 C for 5 hours, a porosity provided by pores having a diameter of at most 200 nm which is at least 0.15 cm3/g, more particularly at least 0.2 cm3/g. Moreover, these same compositions may have, after calcining at 1000 C for 5 hours, a porosity of at least 0.10 cm3/g, more particularly of at least 0.15 cm3/g;
this porosity being provided by pores having a diameter of at most 50 nm.
It should also be noted that the compositions of the invention have substantially identical porosities after calcining at 900 C for 5 hours. In other words, the porosity of the compositions of the invention practically does not vary after calcining at 900 C then at 1000 C for 5 hours. This applies most particularly to the porosity provided by the pores of at most 200 nm. Specifically, in this case, the reduction in the porosity is generally at most 10%, preferably at most 5%.
The method for preparing the composition of the invention will now be described.
This method is characterized in that it comprises the following steps:
- a liquid medium comprising a cerium compound is formed;
- the medium is heated at a temperature of at least 100 C;
- the precipitate obtained at the end of the preceding step is separated from the liquid medium, a compound of the other rare earth is added thereto and another liquid medium is formed;
- the medium thus obtained is heated at a temperature of at least 100 C;
- the reaction medium obtained at the end of the preceding heating step is brought to a basic pH; and - the precipitate derived from the preceding step is separated and is calcined.
The first step of the method therefore consists in forming a liquid medium comprising a cerium compound.
The liquid medium is generally water.
The cerium compound is preferably chosen from soluble compounds. It may especially be an organic or inorganic acid salt such as a nitrate, a sulphate, an acetate, a chloride or a ceric ammonium nitrate.
Preferably, ceric nitrate is used. It is advantageous to use salts with a purity of at least 99.5o and more particularly of at least 99.9%. An aqueous ceric nitrate solution can, for example, be obtained by reaction of nitric acid with a hydrated ceric oxide prepared conventionally by reaction of a solution of a cerous salt, for example cerous nitrate, and of an aqueous ammonia solution in the presence of aqueous hydrogen peroxide solution. It is also possible, preferably, to use a ceric nitrate solution obtained according to the method for electrolytic oxidation of a cerous nitrate solution, as described in the document FR-A-2 570 087, and which constitutes in this instance an advantageous starting material.
It should be noted in this instance that the aqueous solutions of cerium salts may exhibit a degree of initial free acidity which can be adjusted by the addition of a base or of an acid. However, it is just as possible to use an initial solution of cerium salts effectively exhibiting a degree of free acidity as mentioned above, as solutions which will have been neutralized beforehand more or less exhaustively. This neutralization can be carried out by addition of a basic compound to the abovementioned mixture, so as to limit this acidity. This basic compound can, for example, be an aqueous ammonia solution or else a solution of alkali metal (sodium, potassium, and the like) hydroxides but preferably an aqueous ammonia solution.
Finally, it should be noted that, when the starting mixture comprises cerium mainly in the III form, it is preferable to involve, in the course of the method, an oxidizing agent, for example aqueous hydrogen peroxide solution.
It is also possible to use a sol as starting compound for the cerium. The term "sol" denotes any system composed of fine solid particles of colloidal dimensions, that is to say of dimensions between approximately 1 nm and approximately 500 nm, based on a cerium compound, this compound generally being a cerium oxide and/or a hydrated cerium oxide in suspension in a liquid aqueous phase, it additionally being possible for said particles optionally to comprise residual amounts of bonded or adsorbed ions, such as, for example, nitrates, acetates, chlorides or ammoniums. It should be noted that, in such a sol, the cerium may be found either completely in the form of colloids or simultaneously in the form of ions and in the form of colloids.
The mixture can without distinction be obtained either from compounds initially in the solid state which will be subsequently introduced into the bottom of a water vessel, for example, or else directly from solutions of these compounds.
The second step of the method consists in heating the medium prepared in the preceding step at a temperature of at least 100 C.
The temperature at which the medium is heated is generally between 100 C and 150 C, and more particularly between 110 C and 130 C. The heating operation can be carried out by introducing the liquid medium into a sealed chamber (closed reactor of the autoclave type). Under the temperature conditions given above, and in an aqueous medium, it is thus possible to specify, by way of illustration, that the pressure in the closed reactor can vary between a value of greater than 1 bar (105 Pa) and 165 bar (1.65 x 10' Pa), preferably between 5 bar (5 x 10s Pa) and 165 bar (1.65 x 10 7 Pa). The heating can also be carried out in an open reactor for temperatures in the vicinity of 100 C.
The heating can be carried out either in air or under an inert gas atmosphere, preferably nitrogen.
The duration of the heating can vary within wide limits, for example between 30 minutes and 48 hours, preferably between 1 and 5 hours. Likewise, the rise in temperature is carried out at a rate which is not critical and it is thus possible to reach the reaction temperature set by heating the medium, for example, between 30 minutes and 4 hours, these values being given entirely by way of indication.
At the end of the heating step a precipitate is obtained which is separated from the liquid medium by any suitable means, for example by decanting the mother liquors.
Added to the precipitate thus separated is a compound of the other rare earth, forming a second liquid medium.
The rare-earth compound may be of the same nature as the cerium compound used in the first step of the method.
That which has been described above for this compound therefore applies here to the rare-earth compound which may more particularly be chosen from nitrates, sulphates, acetates and chlorides.
In another step of the method, the second liquid medium is heated at a temperature of at least 100 C.
Here too, that which has been described above for the first heating step likewise applies here for the second heating step.
At the end of this second heating step, the reaction medium obtained is brought to a basic pH. In order to do this, a basic compound is introduced into the reaction medium. It is possible to use, as a base or basic compound, hydroxide type products. Mention may be made of alkali or alkaline-earth metal hydroxides. It is also possible to use secondary, tertiary or quaternary amines. However, amines and aqueous ammonia may be preferred insofar as they reduce the risks of contamination by the alkali or alkaline-earth metal cations. Mention may also be made of urea. The basic compound may more particularly be used in the form of a solution.
The pH value to which the medium is brought may more particularly be between 8 and 10, more particularly 8 and 9.
In a final step of the method according to the invention, the precipitate recovered is subsequently calcined. This calcining makes it possible to develop the crystallinity of the product formed and it can also be adjusted and/or chosen according to the subsequent operating temperature intended for the composition according to the invention, this being done while taking into account the fact that the specific surface area of the product decreases as the calcining temperature employed increases. Such a calcination is generally carried out in air but a calcination carried out, for example, in an inert gas or in a controlled atmosphere (oxidizing or reducing) is very clearly not excluded.
In practice, the calcining temperature is generally limited to a range of values of between 300 C and 1000 C.
The compositions of the invention can be used as catalysts or catalyst supports. Thus, the invention also relates to catalytic systems comprising the compositions of the invention. For such systems, these compositions can thus be applied to any support commonly used in the field of catalysis, that is to say thermally inert supports in particular. This support can be chosen from alumina, titanium oxide, zirconium oxide, silica, spinels, zeolites, silicates, crystalline silicoaluminium phosphates or crystalline aluminium phosphates.
The compositions can also be used in catalytic systems comprising a coating (wash coat) possessing catalytic properties and based on these compositions, on a substrate of the, for example, metal or ceramic monolith type. The coating can itself also comprise a support of the type of those mentioned above. This coating is obtained by mixing the composition with the support, so as to form a suspension which can subsequently be deposited on the substrate.
These catalytic systems and more particularly the compositions of the invention can have a great many applications. They are therefore particularly well suited to, and thus usable in, the catalysis of various reactions, such as, for example, dehydration, hydrosulphurization, hydrodenitrification, desulphurization, hydrodesulphurization, dehydrohalogenation, reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, dismutation, oxychlorination, dehydrocyclization of hydrocarbons or other organic compounds, oxidation and/or reduction reactions, the Claus reaction, treatment of exhaust gases from internal combustion engines, diesel or petrol engines, demetallation, methanation, the shift conversion or water gas shift or the catalytic oxidation of the soot emitted by internal combustion engines, such as diesel engines or petrol engines operating under lean burn conditions. Finally, the catalytic systems and the compositions of the invention can be used as NOX traps or for promoting the reduction of NOX, even in an oxidizing environment.
In the case of these uses in catalysis, the compositions of the invention are employed in combination with precious metals. They thus act as support for these metals. The nature of these metals and the techniques for the incorporation of the latter in the support compositions are well known to a person skilled in the art. For example, the metals can be platinum, rhodium, palladium or iridium.
They can in particular be incorporated in the compositions by impregnation.
Among the uses mentioned, treatment of the exhaust gases from internal combustion engines (automobile postcombustion catalysis) constitutes a particularly advantageous application. For this reason, the invention also relates to a method for treating the exhaust gases from internal combustion engines which is characterized in that use is made, as catalyst, of a catalytic system as described above or of a composition according to the invention and as described above.
Examples Examples will now be given.
This example relates to the preparation of a composition based on cerium oxide and on lanthanum oxide in a proportion, by weight of oxide, of 90/10 respectively.
200 ml of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.1 ml of a 25% aqueous ammonia solution, then diluted with 794.9 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 20.5 ml of a lanthanum nitrate solution containing 5.16 g of La203 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The solution was then heated at 120 C for 2 hours. After cooling the solution to 85 C, a 25% aqueous ammonia solution was added, with stirring, in order to adjust the pH to 8.5. The suspension obtained was filtered over a Nutsche filter to obtain a precipitate. The precipitate was calcined in air at 300 C for 10 hours to obtain a composition containing 10 wt% of La203 and 90 wt%
of Ce02.
This example relates to the preparation of a composition based on cerium oxide and on praseodymium oxide in a proportion, by weight of oxide, of 90/10 respectively.
197.6 of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.6 ml of a 25% aqueous ammonia solution, then diluted with 796.8 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 11.0 ml of a praseodymium nitrate solution containing 5.25 g of Pr6011 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The procedure as in Example 1 was then followed to obtain a composition containing 10 wt% of Pr6011 and 90 wt% of Ce02 .
This example relates to the preparation of a composition based on cerium oxide, lanthanum oxide and praseodymium oxide in a proportion, by weight of oxide, of 90/5/5 respectively.
201.6 ml of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.7 ml of a 25% aqueous ammonia solution, then diluted with 792.7 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 6.1 ml of a lanthanum nitrate solution containing 2.63 g of La203 and 5.3 ml of a praseodymium nitrate solution containing 2.63 g of Pr6011 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The procedure as in Example 1 was then followed to obtain a composition containing 5 wt% of La203, 5 wt% of Pr6011 and 90 wt% of Ce02.
This example relates to the preparation of a composition based on cerium oxide and lanthanum oxide in a proportion by weight of oxide of 80/20 respectively.
197.6 ml of a ceric nitrate solution containing at least 90 mol% of cerium IV ions and containing 50 g of CeO2 were neutralized with 5.6 ml of a 25% aqueous ammonia solution, then diluted with 796.8 ml of pure water. This solution was then heated at 100 C for 0.5 hour. After removing the mother liquors, 46.1 ml of a lanthanum nitrate solution containing 11.60 g of La203 were added to the medium. Pure water was added to bring the total volume of the solution to 1 litre. The procedure as in Example 1 was then followed to obtain a composition containing 20 wt% of La203 and 80 wt% of Ce02 .
This example relates to the preparation, by a coprecipitation method, of a composition based on cerium oxide and lanthanum oxide in a proportion, by weight of oxide, of 90/10 respectively.
35.5 ml of a cerous nitrate solution containing 18 g of CeOzr 7.9 ml of a lanthanum nitrate solution containing 2.0 g of La2O3 and 356.6 ml of pure water were mixed together.
Introduced into this mixture were 400 ml of a 10% aqueous ammonia solution over 10 minutes, with stirring, to precipitate cerium and lanthanum hydroxides. The pH after precipitation was 10. The precipitate was filtered over a Nutsche filter and calcined in air at 300 C for 10 hours to obtain a composition containing 10 wt% of La2O3 and 90 wt%
of CeO2.
This example relates to the preparation, by a coprecipitation method, of a composition based on cerium oxide and praseodymium oxide in a proportion, by weight of oxide, of 90/10 respectively.
35.5 ml of a cerous nitrate solution containing 18 g of Ce02r 4.0 ml of a praseodymium nitrate solution containing 2.0 g of Pr6011 and 360.5 ml of pure water were mixed together. Introduced into this mixture were 400 ml of a 10%
aqueous ammonia solution over 10 minutes, with stirring, to precipitate cerium and praseodymium hydroxides. The pH
after precipitation was 10. The procedure as in Comparative Example 5 was then followed to obtain a composition containing 10 wt% of Pr6011 and 90 wt% of Ce02.
This example relates to the preparation, by a coprecipitation method, of a composition based on cerium oxide, lanthanum oxide and praseodymium oxide in a proportion, by weight of oxide, of 90/5/5 respectively.
35.5 ml of a cerous nitrate solution containing 18 g of CeO2, 4.0 ml of a lanthanum nitrate solution containing 1.0 g of La203r 2.0 ml of a praseodymium nitrate solution containing 1.0 g of Pr6011 and 358.5 ml of pure water were mixed together. Introduced into this mixture were 400 ml of a 10% aqueous ammonia solution over 10 minutes, with stirring, to precipitate cerium and praseodymium hydroxides.
The pH after precipitation was 10. The procedure as in Comparative Example 5 was then followed to obtain a composition containing 5 wt% of La203, 5 wt% of Pr6011 and 90 wt% of CeOZ .
Given in Table 1 below are the specific surface areas of the products from the various examples.
Table 1 Specific surface area (m /g) Example 300 C 10 900 C 5 h 1000 C 5 1100 C 5 h h h comparative 6 70 6 2 < 1 comparative 7 71 7 3 < 1 comparative Given in Table 2 below are the porosity characteristics of the products from the various examples.
These porosities were measured with a CE Instruments Pascal 240 machine.
. _., _. .~v ~.., ......,VV
Table 2 Porosity (CM3 /g) After calcination 900 C After calcination 5h 1000 C 5h Porosity Porosity Porosity Example Porosity provided provided provided provided by by pores by pores by pores pores of at of at of at most of at most most 200 nm most 50 200 nm 50 nm nm 1 0.21 0.19 0.20 0.17 2 0.23 0.20 0.22 0.15 3 0.25 0.21 0.24 0.19 4 0.21 0.19 0.22 0.18 0.08 0.06 0.06 0.02 comparative 6 0.06 0.04 0.05 0.03 comparative 7 0.07 0.05 0.06 0.04 comparative
Claims (14)
1. Composition mainly consisting of cerium oxide and of at least one oxide of another rare earth, wherein said composition has a specific surface area of at least 20 m2/g to 25 m2/g after calcining at 1000°C for 5 hours.
2. Composition according to Claim 1, wherein said composition has a specific surface area of at least 22 m2/g after calcining at 1000°C for 5 hours.
3. Composition according to Claim 1 or 2, wherein said composition has a specific surface area of at least 10 m2/g after calcining at 1100°C for 5 hours.
4. Composition according to Claim 3, wherein said composition has a specific surface area of at least 14 m2/g after calcining at 1100°C for 5 hours.
5. Composition according to any one of claims 1 to 4, wherein said composition has a specific surface area of at least 30 m2/g after calcining at 900°C for 5 hours.
6. Composition according to any one of claims 1 to 5, wherein the other rare earth is yttrium, neodymium, lanthanum, praseodymium or these last two elements in combination.
7. Composition according to any one of claims 1 to 6, wherein said composition has, after calcining at 1000°C for 5 hours, a porosity of at least 0.15 cm3/g, provided by pores having a diameter of at most 200 nm.
8. Composition according to any one of claims 1 to 6, wherein said composition has, after calcining at 1000°C for 5 hours, a porosity of at least 0.2 cm3/g provided by pores having a diameter of at most 200 nm.
9. Composition according to any one of claims 1 to 6, wherein said composition has, after calcining at 1000 C for 5 hours, a porosity of at least 0.10 cm3/g, provided by pores having a diameter of at most 50 nm.
10. Composition according to any one of claims 1 to 6, wherein said composition has, after calcining at 1000 C for 5 hours, a porosity of at least 0.15 cm3/g provided by pores having a diameter of at least 50 nm.
11. Method for preparing a composition according to any one of claims 1 to 10, comprising the following steps:
- a liquid medium comprising a cerium compound is formed;
- the medium is heated at a temperature of at least 100 C thereby a first precipitate is obtained;
-said first precipitate is separated from the liquid medium, a compound of the other rare earth is added thereto and another liquid medium is formed;
- said another liquid medium is heated at a temperature of at least 100 C thereby a reaction medium is obtained;
- said reaction medium is brought to a basic pH thereby a second precipitate is obtained; and - said second precipitate is separated and is calcined.
- a liquid medium comprising a cerium compound is formed;
- the medium is heated at a temperature of at least 100 C thereby a first precipitate is obtained;
-said first precipitate is separated from the liquid medium, a compound of the other rare earth is added thereto and another liquid medium is formed;
- said another liquid medium is heated at a temperature of at least 100 C thereby a reaction medium is obtained;
- said reaction medium is brought to a basic pH thereby a second precipitate is obtained; and - said second precipitate is separated and is calcined.
12. Method according to claim 11, wherein use is made, as compounds of cerium and of the other rare earth, of a compound chosen from nitrates, sulphates, acetates, chlorides or ceric ammonium nitrate.
13. Catalytic system, wherein the catalytic system comprises a composition according to any one of claims 1 to 10.
14. Method for treating the exhaust gases of internal combustion engines, wherein use is made, as catalyst, of a catalytic system according to claim 13 or of a composition according to any one of claims 1 to 10.
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FR07/04400 | 2007-06-20 | ||
PCT/JP2008/061689 WO2008156219A1 (en) | 2007-06-20 | 2008-06-20 | High specific surface area mixed oxide of cerium and of another rare earth, preparation method and use in catalysis |
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FR2852596B1 (en) | 2003-03-18 | 2007-02-23 | Rhodia Elect & Catalysis | COMPOSITION BASED ON CERIUM AND ZIRCONIUM OXIDES WITH A SPECIFIC SURFACE STABLE BETWEEN 900 ° C AND 1000 ° C, PROCESS FOR PREPARING THE SAME AND USE THEREOF AS A CATALYST |
JP2006256911A (en) * | 2005-03-17 | 2006-09-28 | Tosoh Corp | Preparation method of ceria-zirconia-based oxide |
JP4869647B2 (en) * | 2005-07-14 | 2012-02-08 | 住友大阪セメント株式会社 | Method for producing rare earth element-added cerium oxide powder |
JP5344805B2 (en) * | 2006-06-20 | 2013-11-20 | 第一稀元素化学工業株式会社 | Zirconia-based composite oxide and method for producing the same |
JP5100244B2 (en) * | 2006-10-12 | 2012-12-19 | 第一稀元素化学工業株式会社 | Zirconia / ceria / yttria composite oxide and method for producing the same |
JP5279183B2 (en) * | 2006-10-12 | 2013-09-04 | 第一稀元素化学工業株式会社 | Method for producing cerium-based oxide |
FR2917646B1 (en) | 2007-06-20 | 2011-06-03 | Anan Kasei Co Ltd | MIXED OXIDE WITH HIGH SURFACE SPECIFIC OF CERIUM AND OTHER RARE EARTH, PROCESS FOR PREPARATION AND USE IN CATALYSIS |
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JP2010530343A (en) | 2010-09-09 |
CA2691299A1 (en) | 2008-12-24 |
KR101216021B1 (en) | 2012-12-28 |
KR101158272B1 (en) | 2012-06-19 |
US8435919B2 (en) | 2013-05-07 |
EP2160357A1 (en) | 2010-03-10 |
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DK2160357T3 (en) | 2021-10-11 |
RU2010101675A (en) | 2011-07-27 |
US20100329954A1 (en) | 2010-12-30 |
WO2008156219A1 (en) | 2008-12-24 |
KR20120031315A (en) | 2012-04-02 |
CN101687661A (en) | 2010-03-31 |
JP5148637B2 (en) | 2013-02-20 |
KR20100022501A (en) | 2010-03-02 |
FR2917646B1 (en) | 2011-06-03 |
FR2917646A1 (en) | 2008-12-26 |
CN101687661B (en) | 2013-11-13 |
EP2160357A4 (en) | 2013-05-01 |
RU2445268C2 (en) | 2012-03-20 |
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